Deform an array of objects without modifying its geometry, just the relative position of them
You can use a "dummy" object to parent your array object to.

Here I've created a two dimensional array of planes and applied two Curve Modifiers... one the for the X and one for the Y direction:



Once that's done, create one instance of your object and parent it to the plane array by going to Object Properties and selecting the plane.

Right Click on the plane and enable duplication with "Faces" as the method.  This will create an instance of the child (sphere) for every face of the plane array.  You can manipulate the curves under the plane to give you the desired bend.







EDIT: An alternative would be to apply and separate the array elements and use the Proportional Editing Tool to position them:

1.) Apply the Array Modifiers

2.) Go into Edit Mode and Select All by pressing A twice.

3.) Press P and separate by Loose Parts

4.) Go back to Object Mode, select all the new Objects, and set their origins to the center of the spheres: Shift Ctrl Alt C

5.) Select the middle sphere and enable Proportional Editing in the toolbar.

6.) Translate the sphere in the Z-direction and use the scroll-wheel to adjust the size of the Proportional Translation.